Magnetic shielding using electrical steel panels at extremely low frequencies

A new test method and finite element modelling were used to investigate how material properties of electrical steel panels affect their shielding factors. Both experiment and modelling showed an improved DC shielding factor with increasing thickness for the shields of similar magnetic properties. Enhanced shielding by the eddy currents was demonstrated by testing the same steel panel under AC and DC field conditions. Comparing to non-oriented steel panels, a decreasing shielding factor with the frequency from 50 Hz to 400 Hz was found for grain-oriented steels. This was also investigated by measuring magnetizations along rolling and transverse directions within the panels. It was found that measured shielding factors of double-layer shields with two grain-oriented steel panels could be improved significantly with orthogonally arranged rolling directions. Different shielding factors were found by placing different panel closer to the field source in the test of double-layer shields formed by one grain-oriented and one non-oriented steel panels. Although little shielding effect of aluminium panels are found at 50 Hz, adding the same aluminium panel with single electrical steel shield was dramatically improved the shielding. The magnetization of shielding sample at AC conditions has been modelled and measured. The magnetization was found very low due to the demagnetizing effect. Therefore, the permeability at very low magnetization range has a large effect on the magnetic shielding factors of the steel panels. Drilled hole as a defect in the panel and overlap of the panels have been tested with the new test method. Small hole in the panel would not cause the degradation of the overall shielding factor of the shield rooms. Overlap was proved to be an effective way to reduce the flux leakage at the joints between the panels The difference between the computed and measured shielding factors is addressed by analysing the capability of the solver used in the finite element modelling and the uncertainty of the measured B-H characteristic of the material as the input to the model

Energy-Efficient UAV Communications in the Presence of Wind: 3D Modeling and Trajectory Design

The rapid development of unmanned aerial vehicle (UAV) technology provides flexible communication services to terrestrial nodes. Energy efficiency is crucial to the deployment of UAVs, especially rotary-wing UAVs whose propulsion power is sensitive to the wind effect. In this paper, we first derive a three-dimensional (3D) generalised propulsion energy consumption model (GPECM) for rotary-wing UAVs under the consideration of stochastic wind modeling and 3D force analysis. Based on the GPECM, we study a UAV-enabled downlink communication system, where a rotary-wing UAV flies subject to stochastic wind disturbance and provides communication services for ground users (GUs). We aim to maximize the energy efficiency (EE) of the UAV by jointly optimizing the 3D trajectory and user scheduling among the GUs based on the GPECM. We formulate the problem as stochastic optimization, which is difficult to solve due to the lack of real-time wind information. To address this issue, we propose an offline-based online adaptive (OBOA) design with two phases, namely, an offline phase and an online phase. In the offline phase, we average the wind effect on the UAV by leveraging stochastic programming (SP) based on wind statistics; then, in the online phase, we further optimize the instantaneous velocity to adapt the real-time wind. Simulation results show that the optimized trajectories of the UAV in both two phases can better adapt to the wind in changing speed and direction, and achieves a higher EE compared with the windless scheme. In particular, our proposed OBOA design can be applied in the scenario with dramatic wind changes, and makes the UAV adjust its velocity dynamically to achieve a better performance in terms of EE.Comment: 31 pages, 13 figure

Effect of geometric factors on the energy performance of high-rise office towers in Tianjin, China

To improve energy efficiency of office buildings in Tianjin, we select a prototypical high-rise office tower as an example and focus on the effect of geometric factors on building energy performance. These factors include the orientation, plane shape, floor area, plane shape factor (the ratio of the plane length to the plane width, only as regards to a rectangle-shaped plane), floor height, floor number and window-to-wall ratio. The simulation is performed in DesignBuilder, which integrates artificial lighting with instantaneous daylight during the energy simulation process. The geometric factors of the defined prototype are examined in both single-parameter and multi-parameter evaluations. As to the multi-parameter results, the energy saving rate can vary by up to 18.9%, and reducing the floor height is observed to be the most effective means of reducing annual total end-use energy consumption, followed by increasing the plane shape factor and reducing the floor area. The results can serve as a reference for passive design strategies related to geometric factors in the early design stage